Patchy Environment Research Articles

Whence the Gosport Sand (Upper Middle Eocene, Alabama)? The Origin of Glauconitic Shell Beds In the Paleogene of the U.S. Gulf Coastal Plain

ABSTRACT: An explanation for the depositional history of the Gosport Sand has proven to be as puzzling as its diverse mollusk fossils is beguiling. We propose that shifting delta lobes produced patchy environments which accumulated to form the Gosport Sand and likely other glauconite- and fossil-rich shell beds of the Gulf Coastal Plain of the Paleogene. We present facies and mineralogical data to suggest glauconite in the Gosport Sand was deposited during relatively stable environmental conditions. Increased glauconite maturity and taphonomic alteration in the Gosport Sand are attributed to eustatic transgression, resulting in decreased deposition, enhanced winnowing, and increased exposure at the sediment–water interface. Increased fossil diversity and abundance likely result from time-averaging and accumulation of shells from ancient patchy habitats analogous to modern “inner shallow shelf” and “open sound” environments. Delta progradation and subsidence would have determined the migration of these environments. We evoke a similar depositional model for glauconite-rich shell beds distributed throughout the Paleocene and Eocene of the Gulf Coastal Plain based on their transgressive nature and roughly equivalent facies. These shifting environmental conditions may have played a partial role in generating the high molluscan diversity of the Gulf Coastal Plain of the Paleogene.

Phenomapping of rangelands in South Africa using time series of RapidEye data

Phenomapping is an approach which allows the derivation of spatial patterns of vegetation phenology and rangeland productivity based on time series of vegetation indices. In our study, we propose a new spatial mapping approach which combines phenometrics derived from high resolution (HR) satellite time series with spatial logistic regression modeling to discriminate land management systems in rangelands. From the RapidEye time series for selected rangelands in South Africa, we calculated bi-weekly noise reduced Normalized Difference Vegetation Index (NDVI) images. For the growing season of 2011⿿2012, we further derived principal phenology metrics such as start, end and length of growing season and related phenological variables such as amplitude, left derivative and small integral of the NDVI curve. We then mapped these phenometrics across two different tenure systems, communal and commercial, at the very detailed spatial resolution of 5m. The result of a binary logistic regression (BLR) has shown that the amplitude and the left derivative of the NDVI curve were statistically significant. These indicators are useful to discriminate commercial from communal rangeland systems. We conclude that phenomapping combined with spatial modeling is a powerful tool that allows efficient aggregation of phenology and productivity metrics for spatially explicit analysis of the relationships of crop phenology with site conditions and management. This approach has particular potential for disaggregated and patchy environments such as in farming systems in semi-arid South Africa, where phenology varies considerably among and within years. Further, we see a strong perspective for phenomapping to support spatially explicit modelling of vegetation.

Mesoscale and high-frequency variability of macroscopic particles (> 100 μm) in the Ross Sea and its relevance for late-season particulate carbon export

The Ross Sea plays a major role in the transfer of organic carbon from the surface into the deep sea due to the combination of high seasonal productivity and Antarctic bottom water formation. Here we present a particle inventory of the Ross Sea based on a combined deployment of a video particle profiler (VPP) and a high-resolution digital holographic microscope (DIHM). Long-distance (100s of kilometers) and short-distance (10s of kilometers) sections showed high variability of particle distributions that co-varied with the density structure of the water column. Particle export was apparent at sites of locally weakened pycnoclines, likely an indirect effect of nutrient mixing into the surface layer and local blooms that lead to export. Particle volume abundances at 200–300m depth were highly correlated with particle volume abundances in the upper mixed layer (<60m), consistent with particles at depth primarily the result of export rather than lateral advection. Phaeocystis antarctica (Haptophyta) colonies that were initially retained in the mixed layer sank below the euphotic zone within a period of two weeks. Fine-scale analysis at a resolution<1m revealed a significantly overdispersed (i.e., highly patchy) environment in all casts. Patchiness, as determined by the Lloyd index of patchiness and the Index of Aggregation, increased in and below the pycnocline presumably due to aggregation of particles while accumulating on density gradients. In contrast, particles in the upper mixed layer and in the nepheloid layers were more randomly distributed. In 40 of the 84 VPP depth profiles, a periodicity of particle peaks ranged from 10 to 90m with a mode of 30m, which can be regarded as the “relevant scale” or “characteristic patch size” of the vertical distribution of particles. While chlorophyll fluorescence and particle mass determined by VPP were significantly correlated at higher particle abundances, the relationship changed from cast to cast, reflecting changes in the relative contribution of fresh phytoplankton to total particle mass. Particles that sank below the main pycnocline were composed of phytoplankton, marine snow with and without embedded phytoplankton, crustacean plankton, and a surprisingly high percentage of heterotrophic (and perhaps mixotrophic) protists, such as acantharians and tintinnids.

Identifying management actions to increase foraging opportunities for shorebirds at semi‐intensive shrimp farms

Summary The expansion of aquaculture has resulted in widespread habitat conversion throughout the world. Identifying beneficial management measures may dramatically reduce negative impacts of aquaculture for migratory birds. We studied how densities of foraging shorebirds varied at ponds within a semi‐intensive shrimp aquaculture farm on the north‐western coast of Mexico, as related to timing of harvest and tidal cycles. Further, we estimated the total daily available area for each shorebird species throughout two entire harvesting seasons at the shrimp farm. High densities (average ca. 50 individuals per ha) of foraging shorebirds were found during the first days following pond harvest. The most abundant species were Willet Tringa semipalmata and Black‐necked Stilt Himantopus mexicanus, followed by Marbled Godwit Limosa fedoa and American Avocet Recurvirostra americana. Other regular, but less abundant, species were whimbrel Numenius phaeopus and dowitchers Limnodromus spp. Densities of shorebirds sharply declined daily following harvest. In addition, the time‐window availability of harvested ponds was related to each species' foraging behaviour: &lt;2 days for godwits and dowitchers, 4 days for stilts, 5 days for willets and more than a week for avocets and whimbrels. However, birds continued to use harvested ponds that received a low, but continuous water influx. Our results demonstrate that a tropical shrimp farm represents a patchy environment that provides 4·3–12·7% (depending on species) of its total area as foraging opportunities for shorebirds. Synthesis and applications. Sequential harvesting of shrimp aquaculture farm ponds and increasing moisture of the substrate by providing some water supply to harvested ponds, at least throughout the harvesting period, could integrate shorebird conservation into shrimp‐farm production. These low‐cost and easy management procedures would not increase costs or affect shrimp production – thus representing a win‐win opportunity – and would have potential applications for shorebird conservation throughout the world.

Mechanisms That Generate Resource Pulses in a Fluctuating Wetland.

Animals living in patchy environments may depend on resource pulses to meet the high energetic demands of breeding. We developed two primary a priori hypotheses to examine relationships between three categories of wading bird prey biomass and covariates hypothesized to affect the concentration of aquatic fauna, a pulsed resource for breeding wading bird populations during the dry season. The fish concentration hypothesis proposed that local-scale processes concentrate wet-season fish biomass into patches in the dry season, whereas the fish production hypothesis states that the amount of dry-season fish biomass reflects fish biomass production during the preceding wet season. We sampled prey in drying pools at 405 sites throughout the Florida Everglades between December and May from 2006–2010 to test these hypotheses. The models that explained variation in dry-season fish biomass included water-level recession rate, wet-season biomass, microtopography, submerged vegetation, and the interaction between wet-season biomass and recession rate. Crayfish (Procambarus spp.) biomass was positively associated with wet-season crayfish biomass, moderate water depth, dense submerged aquatic vegetation, thin flocculent layer and a short interval of time since the last dry-down. Grass shrimp (Palaemonetes paludosus) biomass increased with increasing rates of water level recession, supporting our impression that shrimp, like fish, form seasonal concentrations. Strong support for wet-season fish and crayfish biomass in the top models confirmed the importance of wet-season standing stock to concentrations of fish and crayfish the following dry season. Additionally, the importance of recession rate and microtopography showed that local scale abiotic factors transformed fish production into the high quality foraging patches on which apex predators depended.

Root morphology and mycorrhizal symbioses together shape nutrient foraging strategies of temperate trees.

Photosynthesis by leaves and acquisition of water and minerals by roots are required for plant growth, which is a key component of many ecosystem functions. Although the role of leaf functional traits in photosynthesis is generally well understood, the relationship of root functional traits to nutrient uptake is not. In particular, predictions of nutrient acquisition strategies from specific root traits are often vague. Roots of nearly all plants cooperate with mycorrhizal fungi in nutrient acquisition. Most tree species form symbioses with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi. Nutrients are distributed heterogeneously in the soil, and nutrient-rich "hotspots" can be a key source for plants. Thus, predicting the foraging strategies that enable mycorrhizal root systems to exploit these hotspots can be critical to the understanding of plant nutrition and ecosystem carbon and nutrient cycling. Here, we show that in 13 sympatric temperate tree species, when nutrient availability is patchy, thinner root species alter their foraging to exploit patches, whereas thicker root species do not. Moreover, there appear to be two distinct pathways by which thinner root tree species enhance foraging in nutrient-rich patches: AM trees produce more roots, whereas EM trees produce more mycorrhizal fungal hyphae. Our results indicate that strategies of nutrient foraging are complementary among tree species with contrasting mycorrhiza types and root morphologies, and that predictable relationships between below-ground traits and nutrient acquisition emerge only when both roots and mycorrhizal fungi are considered together.

Nitrogen dynamics within and between decomposing leaves, bark and branches in Eucalyptus planted forests

Nitrogen transfer between litter components is often presented as a key mechanism responsible for the synergistic effect of litter mixtures on decomposition rates. The litter cover is a heterogeneous environment stemming from the input of chemically distinct materials and the transfer of nutrients in this patchy environment is likely to fulfil the specific needs of microbial communities in each micro-environment. Our study aimed to gain insight into the factors controlling N dynamics within and between leaves and woody components in the litter cover. We used 15N labelling to discriminate endogenous and exogenous N and to measure N transfers between three types of litter components, viz. leaves and twigs (L + T), bark and branches, in 162 litter bags for more than 2 years in two Congolese Eucalyptus forests with contrasting N status (low-N vs high-N litter). Large quantities of N were released from N-rich L + T at the end of the study while early release of leachable N was only observed for the high-N L + T. Exogenous N was only incorporated in N-poor litter components (bark and branches) and a net increase in N compared to the initial quantities only occurred in the low-N bark. The bi-directional N transfers observed between litter components were most likely microbially-mediated rather than driven by abiotic leaching. Nitrogen transfers were controlled by the N status of both source and sink litter components, contrary to the diffusion theory based on concentration gradient. For a given source, more N was transferred to N-rich than to N-poor sink components. Our results suggested that the microbial community might control both the quantity of N available to be transferred to other microsites and the quantity that is actually transferred, presumably because the potential for N immobilization may be limited in N-poor litter components. Interactions among micro-environments can favor chemical convergence from distinct litter components to humified organic matter along the decay continuum.

Establishing precise estimates of abundance in patchy habitats of the marine nearshore

Exploratory investigations of optimal sampling designs are a critical component of the decision-making process in ecology where inherent natural variation can lead to erroneous conclusions if left unexamined. Pilot studies and exploratory analyses that investigate the precision of sampling regimes may reduce the chances of erroneous results and can be used to optimise processing time in larger ecological research programs. In our study, we calculated optimal precision estimates for sampling macroinvertebrates and ichthyofauna in surf-zone wrack accumulations by investigating the precision of the mean for sub-samples of seine nets and also for the number of replicate seine nets to guide future sampling regimes. We discovered that the processing time for individual seine net samples could be reduced by 50% using sub-sampling and that time to process replicate seine net samples could be reduced by 25% while maintaining acceptable precision. In future, we suggest that the use of pilot studies with similar exploratory approaches should be less of an exception and more a critical component of ecological investigations, particularly in under-studied or newly-developing areas of research. Further, these types of exploratory approaches are crucially important in a variety of extremely patchy environments where variability is likely to be high.

Effects of plant defenses and water availability on seasonal foraging preferences of the Nubian Ibex (Capra nubiana)

The study of herbivore patch use has implications for herbivore habitat quality assessment, foraging behaviors, species interactions, and coexistence in patchy environments. This research focuses on the comparison of the effects of two qualitatively different plant defenses, mechanical (thorns) and chemical (tannins), on ibex foraging preferences during different seasons of the year. The occurrence of both chemical and mechanical plant defenses were experimentally manipulated in artificial resource patches, in addition to water availability. Ibex foraging preferences were quantified using giving-up densities during four separate fieldwork sessions in each of the seasons of the year at cliff sites overlooking the Zin Valley of the Negev Highlands. Both mechanical and chemical plant defenses significantly hindered ibex food intake overall. Mechanical and chemical defenses acted as substitutable defenses, meaning that their combined effects were not greater than additive. There were strong seasonal patterns of the amount of food consumed by ibex, further corroborated by comparison to rainfall levels. Seasonality also interacted with the effectiveness of plant defenses. Thorns were especially ineffective in summer, whereas tannins were most effective in spring. Decreases in seasonal food availability and increased marginal value of energy for ibex may have resulted in thorn ineffectiveness, while seasonal changes in the emergence of young foliage may have resulted in the greater springtime tannin effectiveness. Water was not found to mitigate the detrimental effects of tannins through dilution. The implications for decreased constraints on selective pressures on ibex due to the substitutability of plant defenses are discussed.

Hierarchical spatial segregation of two Mediterranean vole species: the role of patch-network structure and matrix composition

According to ecological theory, the coexistence of competitors in patchy environments may be facilitated by hierarchical spatial segregation along axes of environmental variation, but empirical evidence is limited. Cabrera and water voles show a metapopulation-like structure in Mediterranean farmland, where they are known to segregate along space, habitat, and time axes within habitat patches. Here, we assess whether segregation also occurs among and within landscapes, and how this is influenced by patch-network and matrix composition. We surveyed 75 landscapes, each covering 78ha, where we mapped all habitat patches potentially suitable for Cabrera and water voles, and the area effectively occupied by each species (extent of occupancy). The relatively large water vole tended to be the sole occupant of landscapes with high habitat amount but relatively low patch density (i.e., with a few large patches), and with a predominantly agricultural matrix, whereas landscapes with high patch density (i.e., many small patches) and low agricultural cover, tended to be occupied exclusively by the small Cabrera vole. The two species tended to co-occur in landscapes with intermediate patch-network and matrix characteristics, though their extents of occurrence were negatively correlated after controlling for environmental effects. In combination with our previous studies on the Cabrera-water vole system, these findings illustrated empirically the occurrence of hierarchical spatial segregation, ranging from within-patches to among-landscapes. Overall, our study suggests that recognizing the hierarchical nature of spatial segregation patterns and their major environmental drivers should enhance our understanding of species coexistence in patchy environments.

Density-Dependent Selection Revisited: Mechanisms Linking Explanantia and Explananda

Interest in the most general theory of the evolutionary ecology of life histories ever proposed—that of density-independent (r) versus density-dependent (K) selection—peaked in the 1980s and 1990s respectively but declined somewhat thereafter because of arguments over its theoretical coherence and some empirical failures; although as is shown here, not so much as is commonly supposed. In this article, some conceptual analyses and clarification of terms in the conditions for its application (density relative to resources as a variable with spatial, temporal, and niche boundaries fixed), and in the explanantia of the theory (costs and frequencies, stability and instability within and among growing and declining populations, multiple levels of selection, and ultimately homogeneous and patchy environments) are presented. These make intelligible plausible mechanisms (consumption and digestion, production, and reproduction) linking the explanantia and the explananda of the theory that are both theoretically coherent and clarify what predictions it does not and does make including about senescence.

Evidence that sex‐specific signals may support mate finding and limit aggregation in the dung beetle Aphodius fossor

1. In temperate climates, dung is often colonised by several species of endocoprid (dwelling) dung beetles which use pats for feeding, shelter, and reproduction.2. Endocoprid beetles aggregate even when offered patches (dung pats) of consistent age, size, and origin, suggesting that beetles themselves might influence the attractiveness of patches to members of their own species. Both pheromones, and physical changes to the structure of dung pats caused by colonising beetles have been suggested as mechanisms facilitating intraspecific aggregation, but neither of these hypotheses have been empirically tested.3. Using a common European dung beetle (Aphodius fossor L.), we conducted a simple choice experiment designed to test whether (i) earlier colonisation by conspecifics could alter dung attractiveness and (ii) whether attraction was influenced by sex‐specific signals.4. We found that female beetles are repelled by dung colonised by conspecific females and are attracted to dung colonised by conspecific males. Male beetles show no evidence of attraction or repellence for dung colonised by either sex. Neither in females nor males was uncolonised dung found to be significantly more or less attractive than predicted by non‐preference.5. Our results suggest that for A. fossor male‐produced signals may support mate finding in patchy environments, and that female‐produced signals may serve to discourage subsequent colonisation by additional females.

Cumulative effects of an herbivorous ecosystem engineer in a heterogeneous landscape

AbstractForaging by herbivores alters individual plants and vegetation communities directly, and engineering behaviors such as bioturbation (digging and turning soil) and biodeposition (deposition of feces and urine) can affect soils and physical properties that indirectly influence vegetation and other organisms. Patchy environments often concentrate the activities of animals, potentially increasing the magnitude of their impacts on the vegetative community over time. To evaluate the potential for herbivorous engineers to enhance existing heterogeneity, we quantified the direct and indirect effects of a burrowing herbivore, the pygmy rabbit (Brachylagus idahoensis), on soil and vegetation in the sagebrush steppe ecosystem of the western United States, and we evaluated whether the effects were related to duration of occupancy by rabbits. Mounded microtopography (i.e., mima mounds) creates distinct resource islands with relatively tall and dense sagebrush shrubs where pygmy rabbits concentrate burrowing and foraging activities. We quantified soil and vegetation characteristics on mima mounds occupied by rabbits for 1–12 yr and on unoccupied mounds. We expected that browsing would negatively influence slow growing sagebrush shrubs, but that digging and biodeposition would enhance soil nutrients and water infiltration. In addition, we hypothesized that the net effect on sagebrush reproduction would be positive because indirect effects on soil would enhance seed production by mature sagebrush and seedling growth, and because bioturbation would increase seed retention and germination. Pygmy rabbit occupancy had significant cumulative effects on both soil and vegetation properties on occupied mima mounds. Over time, browsing reduced sagebrush canopy cover and percent of individual shrubs that were alive. Soil properties were less influenced by the duration of occupancy of mima mounds than by the localized spatial influence of burrowing; elevated nitrogen levels were associated with burrow entrances. Two measures of sagebrush reproduction (seedling recruitment and inflorescence biomass) increased with duration of burrow occupancy, suggesting that over longer time frames pygmy rabbits enhanced reproduction and recruitment of sagebrush shrubs. Our data demonstrate multiple pathways by which an herbivorous engineer can influence habitat heterogeneity, and they suggest that although pygmy rabbits are inconspicuous on the landscape, the species might play an important role in maintaining and augmenting heterogeneity in the sagebrush steppe.

Serotonin promotes exploitation in complex environments by accelerating decision-making.

BackgroundFast responses can provide a competitive advantage when resources are inhomogeneously distributed. The nematode Caenorhabditis elegans was shown to modulate locomotion on a lawn of bacterial food in serotonin (5-HT)-dependent manners. However, potential roles for serotonergic signaling in responding to food discovery are poorly understood.ResultsWe found that 5-HT signaling in C. elegans facilitates efficient exploitation in complex environments by mediating a rapid response upon encountering food. Genetic or cellular manipulations leading to deficient serotonergic signaling resulted in gradual responses and defective exploitation of a patchy foraging landscape. Physiological imaging revealed that the NSM serotonergic neurons responded acutely upon encounter with newly discovered food and were key to rapid responses. In contrast, the onset of responses of ADF serotonergic neurons preceded the physical encounter with the food. The serotonin-gated chloride channel MOD-1 and the ortholog of mammalian 5-HT1 metabotropic serotonin receptors SER-4 acted in synergy to accelerate decision-making. The relevance of responding rapidly was demonstrated in patchy environments, where the absence of 5-HT signaling was detrimental to exploitation.ConclusionsOur results implicate 5-HT in a novel form of decision-making, demonstrate its fitness consequences, suggest that NSM and ADF act in concert to modulate locomotion in complex environments, and identify the synergistic action of a channel and a metabotropic receptor in accelerating C. elegans decision-making.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-016-0232-y) contains supplementary material, which is available to authorized users.

Spatially heterogeneous populations with mixed negative and positive local density dependence

Identifying the steady states of a population is a key issue in theoretical ecology, that includes the study of spatially heterogeneous populations. There are several examples of real ecosystems in patchy environments where the habitats are heterogeneous in their local density dependence. We investigate a multi-patch model of a single species with spatial dispersal, where the growth of the local population is logistic in some localities (negative density dependence) while other patches exhibit a strong Allee effect (positive density dependence). When the local dynamics is logistic in each patch and the habitats are interconnected by dispersal then the total population has only the extinction steady state and a componentwise positive equilibrium, corresponding to persistence in each patch. We show that animal populations in patchy environments can have a large number of steady states if local density dependence varies over the locations. It is demonstrated that, depending on the network topology of migration routes between the patches, the interaction of spatial dispersal and local density dependence can create a variety of coexisting stable positive equilibria. We give a detailed description of the multiple ways dispersal can rescue local populations from extinction.

The mechanisms of maintenance of biodiversity in patchy environments

The mechanisms of maintenance of biodiversity in patchy environments

Feeding type affects microplastic ingestion in a coastal invertebrate community

Marine litter is one of the problems marine ecosystems face at present, coastal habitats and food webs being the most vulnerable as they are closest to the sources of litter. A range of animals (bivalves, free swimming crustaceans and benthic, deposit-feeding animals), of a coastal community of the northern Baltic Sea were exposed to relatively low concentrations of 10μm microbeads. The experiment was carried out as a small scale mesocosm study to mimic natural habitat. The beads were ingested by all animals in all experimental concentrations (5, 50 and 250beadsmL−1). Bivalves (Mytilus trossulus, Macoma balthica) contained significantly higher amounts of beads compared with the other groups. Free-swimming crustaceans ingested more beads compared with the benthic animals that were feeding only on the sediment surface. Ingestion of the beads was concluded to be the result of particle concentration, feeding mode and the encounter rate in a patchy environment.

Modelling small-scale foraging habitat use in breeding Eurasian oystercatchers (Haematopus ostralegus) in relation to prey distribution and environmental predictors

Detailed knowledge of species distributions at a fine spatial scale is an essential prerequisite for the understanding of ecosystems. However, relating species distributions to environmental variables is difficult, and distribution patterns of mobile benthic top predators can only be estimated at a rough spatial scale using visual cues. This is particularly problematic in systems with strong environmental gradients, such as intertidal habitats. Monitoring predators using GPS tags allows collecting precise spatial data over wide areas and during night time. We collected fine-scale data on prey abundance and quality, sediment composition, inundation time of tidal flats, and foraging distances from nest sites to develop a predictive distribution model for oystercatchers (Haematopus ostralegus) in the Wadden Sea, Germany. This shorebird species was able to identify the patches with high biomass and abundance of its endobenthic prey at a very fine spatial scale. Modelling suggested that prey abundance and biomass were essential for predicting oystercatcher occurrence: the probability of encountering a foraging oystercatcher was higher than expected in areas with >100 cockles per m2 and areas with 80g ash-free dry weight per m2. Our modelling approach also showed that habitat use by oystercatchers was very strongly dependent on abiotic factors, i.e., oystercatchers preferred muddy and low-lying tidal flats with short exposure times close to their breeding sites. Oystercatchers only used patches >4km away from their breeding territories if such patches were particularly prey-rich. This study demonstrates the importance of fine-scale models of predators and environmental predictors in patchy environments. These results have two conclusions with important management implications: (1) fine-scale models of distribution data for predators can provide a valuable indicator of the location of important sites worthy of protection; and (2) abiotic predictors alone are suitable to identify potential valuable feeding sites for oystercatchers without the need for time-consuming collection of prey-base data, even in a coastal zone with strong gradients.

Effect of Spatial Dispersion on Evolutionary Stability: A Two-Phenotype and Two-Patch Model.

In this paper, we investigate a simple two-phenotype and two-patch model that incorporates both spatial dispersion and density effects in the evolutionary game dynamics. The migration rates from one patch to another are considered to be patch-dependent but independent of individual’s phenotype. Our main goal is to reveal the dynamical properties of the evolutionary game in a heterogeneous patchy environment. By analyzing the equilibria and their stabilities, we find that the dynamical behavior of the evolutionary game dynamics could be very complicated. Numerical analysis shows that the simple model can have twelve equilibria where four of them are stable. This implies that spatial dispersion can significantly complicate the evolutionary game, and the evolutionary outcome in a patchy environment should depend sensitively on the initial state of the patches.

An almost periodic epidemic model in a patchy environment

The persistence and extinction of an almost periodic epidemic model in a patchy environment are studied. It is shown that the disease cannot invade the disease-free state if the exponential growth bound is less than zero and can invade if it is greater than zero. It is also shown that there exists an almost periodic solution which is globally attractive when each patch admits the same dispersal rate. Finally, numerical simulations illustrate the above results.